The present invention relates to a semiconductor device and a method for fabricating the same, and more particularly, it relates to a technique to form a plug by filling a contact hole or a via hole with a tungsten film.
Conventionally, a plug of tungsten (tungsten plug) is used for connection between a lower interconnect and an upper interconnect in a semiconductor integrated circuit. A tungsten plug is formed as follows: An adhesion layer of a titanium film or a titanium nitride film is deposited on an interlayer insulating film and on a bottom and a wall of a via hole formed in the interlayer insulating film, a tungsten film is deposited on the adhesion layer by CVD, and thereafter, excessive portions of the adhesion layer and the tungsten film present on the interlayer insulating film are removed by CMP (chemical mechanical polishing).
In forming a tungsten plug, it is particularly significant how accurately a CMP end point is controlled in removing the portions of the adhesion layer and the tungsten film present on the interlayer insulating film by the CMP.
In the case where the CMP end point of the tungsten film cannot be accurately detected, the tungsten film is excessively polished so as to largely increase the contact resistance of the tungsten plug or the tungsten film is insufficiently polished so as to cause short-circuit between adjacent tungsten plugs.
Therefore, for example, Japanese Laid-Open Patent Publication No. 8-139060 discloses a method for detecting an end point in polishing a metal film such as a tungsten film by the CMP. In this end point detecting method, an end point is detected as a time point at which the rotating torque of a substrate holder or a turn table is changed when an interlayer insulating film is exposed through the polishing of an adhesion layer and a metal film.
In the conventional CMP, however, the time point at which the interlayer insulating film is exposed is regarded as the polishing end point, excessive polishing can be easily caused.
Therefore, the following method has been proposed: A polishing end point of a tungsten film is detected by detecting the change of the rotating torque of a substrate holder or a turn table when a film polished by the CMP is changed from the tungsten film to the adhesion layer. Thereafter, time required for polishing the adhesion layer (polishing time) is calculated based on the thickness and the polishing rate of the adhesion layer, so that a time point when the polishing time of the adhesion layer has elapsed can be detected as the CMP end point.
However, there still arises a problem that the CMP end point of the tungsten film cannot be accurately detected.
FIGS. 8A and SB show the relationship between time and rotating torque in the CMP carried out on an adhesion layer deposited by the CVD and a tungsten film deposited by the CVD on the adhesion layer. In the case of FIG. 8A, the rotating torque is abruptly increased, and hence, the change of the polished film from the tungsten film to the adhesion layer can be definitely detected. In contrast, in the case of FIG. 8B, the change of the rotating torque is too small to definitely detect the change of the polished film from the tungsten film to the adhesion layer, namely, the CMP end point of the tungsten film.
When the CMP end point of the tungsten film cannot be definitely detected, the amount of tungsten film to be polished is largely varied, so that the tungsten film can be insufficiently polished or a recess can be formed in the tungsten film.
In consideration of the aforementioned conventional problems, an object of the invention is, in CMP of a multi-layer film composed of a first metal film deposited on an insulating film and on a bottom and a wall of a recess formed in the insulating film and a second metal film deposited on the first metal film, accurately detecting a CMP end point of the second metal film.
In order to achieve the object, the semiconductor device of this invention comprises a first metal film deposited on a bottom and a wall of a recess formed in an insulating film on a semiconductor substrate; and a second metal film filled in the recess on the first metal film, and the second metal film is formed from a polycrystalline tungsten film having a crystal plane of a (110) orientation.
In the semiconductor device of this invention, since the second metal film is formed from the polycrystalline tungsten film having a crystal plane of a (110) orientation, a CMP end point of the second metal film can be accurately detected in carrying out the CMP on the second metal film and the first metal film. Accordingly, excessive polishing and insufficient polishing can be avoided in the CMP.
In the semiconductor device, the crystal plane of the second metal film is preferably oriented with a half-value width of 4 degrees or less.
Thus, the CMP end point of the second metal film can be more accurately detected.
In the semiconductor device, the first metal film preferably includes a titanium film having a crystal plane of a (0002) orientation with a half-value width of 4 degrees or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
In the semiconductor device, the first metal film preferably includes a lower titanium film and an upper titanium nitride film, and the lower titanium film preferably has a thickness of 10 nm or more.
Thus, the crystal orientation of the upper titanium nitride film can be improved, and therefore, the crystal orientation of the tungsten film serving as the second metal film can be definitely improved. As a result, the CMP end point of the second metal film can be more accurately detected.
In the semiconductor device, the first metal film preferably includes a lower titanium film and an upper titanium nitride film, and the upper titanium nitride film is preferably formed from a multi-layer film including a plurality of titanium nitride films each with a thickness of 4 nm or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film and formed on the upper titanium nitride film can be definitely improved. Accordingly, the CMP end point of the second metal film can be more accurately improved.
In the semiconductor device, the first metal film preferably includes a titanium nitride film that is found, through a 2xcex8 method using an in-plane X-ray diffractometer, to have a crystal plane of a (220) orientation with a half-value width of 2 degrees or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
In this case, the titanium nitride film preferably includes carbon in a concentration of 5 wt % or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be more definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
Also in this case, the titanium nitride film is preferably formed by CVD using an organic titanium material.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be more definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
The method for fabricating a semiconductor device of this invention comprises the steps of depositing a first metal film on an insulating film formed on a semiconductor substrate and a bottom and a wall of a recess formed in the insulating film; filling a second metal film in the recess on the first metal film; and removing portions of the second metal film and the first metal film present on the insulating film by CMP, and the second metal film is formed from a polycrystalline tungsten film having a crystal plane of a (110) orientation.
In the method for fabricating a semiconductor device of this invention, since the second metal film is formed from the polycrystalline tungsten film having a crystal plane of a (110) orientation, a CMP end point of the second metal film can be accurately detected in carrying out the CMP on the second metal film and the first metal film. Accordingly, excessive polishing and insufficient polishing can be avoided in the CMP. in the method for fabricating a semiconductor device, the crystal plane of the second metal film is preferably oriented with a half-value width of 4 degrees or less.
Thus, the CMP end point of the second metal film can be more accurately detected.
In the method for fabricating a semiconductor device, the first metal film preferably includes a titanium film having a crystal plane of a (0002) orientation with a half-value width of 4 degrees or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
In the method for fabricating a semiconductor device, the first metal film preferably includes a lower titanium film and an upper titanium nitride film, and the lower titanium film preferably has a thickness of 10 nm or more.
Thus, the crystal orientation of the upper titanium nitride film can be improved, and therefore, the crystal orientation of the tungsten film serving as the second metal film can be definitely improved. As a result, the CMP end point of the second metal film can be more accurately detected.
In the method for fabricating a semiconductor device, the first metal film preferably includes a lower titanium film and an upper titanium nitride film, and the upper titanium nitride film is preferably formed from a multi-layer film including a plurality of titanium nitride films each with a thickness of 4 nm or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film and formed on the upper titanium nitride film can be definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
In the method for fabricating a semiconductor device, the first metal film preferably includes a titanium nitride film that is found, through a 2xcex8 method using an in-plane X-ray diffractometer, to have a crystal plane of a (220) orientation with a half-value width of 2 degrees or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
In this case, the titanium nitride film preferably includes carbon in a concentration of 5 wt % or less.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be more definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.
Also in this case, the titanium nitride film is preferably formed by CVD using an organic titanium material.
Thus, the crystal orientation of the tungsten film serving as the second metal film can be more definitely improved, and hence, the CMP end point of the second metal film can be more accurately detected.